1. Technical Field
The disclosure relates to an expansion Assembly, and more particularly to an expansion Assembly for MIMO (multiple input and multiple output) system.
2. Related Art
In the radio communication (such as WiFi and WiMAX), the transmission distance and the transmission rate are associated with the type of antennas. For example, in order to send or receive radio signals in omni-direction manner, an omni-directional antenna applied with a WiFi model is used. However, in this case, large amounts of electric power are wasted on processing the radio signals in 360 degrees. Therefore, the transmission distance decreases. When a long transmission distance is required, the intensity of the signals become weaker as the transmission distance increases. In this case, the quality of the radio communication might be affected. Furthermore, as only a single antenna is used, the transmission rate is limited.
For addressing the problems as mentioned above, the radio communication using MIMO system has been developed. In the MIMO system, the transmission rate and the transmission quality are improved through the spatial degrees of freedom provided by the antennas for transmitting signals and the antennas for receiving signals. The MIMO system may operate in two primary function modes i.e., a spatial diversity mode and a spatial multiplexing mode.
The principle of the spatial diversity mode lies in that the effects of the attenuations in the channels may be adjusted by the multiple transmitting channels provided by the antennas on the transmitting end or the antennas on the receiving end. Therefore, in the spatial diversity mode, the attenuation in some weak signals may be compensated by selecting or combining the signals in the plurality of independent transmitting channels, so as to obtain the high-quality signals.
The principle of the spatial multiplexing mode lies in that the different data-sequences are transmitted by using multiple antennas. The difference data-sequences are extracted by using the spatial degrees of freedom provided by the antennas on the receiving end. Therefore, in the spatial multiplexing mode, the MIMO system is capable of transmitting a number of data sequences at the same time with one frequency band and one power. By this way, the transmission rate in the radio communication is increased dramatically.
However, for either the spatial diversity mode or the spatial multiplexing mode, once the transmitting distance increases, the quality of the transmission decreases. Although the quality of the signals in the spatial diversity mode can be maintained by selecting the high-quality channels in all the multiple transmitting channels, the fact is that the transmitting distance is difficult to be increased substantially. In the spatial diversity mode, when the transmitting distance increases, a transmitting path with slightly better quality can be selected from the transmitting channels in which all the signals have attenuations.
For increasing the transmitting distance, the radio signals are concentrated in one direction for transmission. However, the method mentioned above lose the advantage of transmitting signals in omni-direction. Therefore, it is difficult to reach balance between the transmitting distance and the omni-directionality for the radio communication module in the MIMO system.